Stress wave drill

ABSTRACT

A method and apparatus for drilling a hole in rock. An openended, hardened, drilling head containing a means for creating high-intensity stress waves capable of spalling rock is utilized to drill the hole. A fluid is passed through the drilling head which removes the spalled rock from the drilling head.

llnited States Patent 1191 Allgood etal;

[ STRESS WAVE DRILL 3,679,007 7/1972 OHare 175/16 [75] Inventors: Jay R. Allgood, Camarillo; Robert J. OTHER PUBLICATIONS Odeno Calabasas both of Steiger, A. 1.; Russian Electric Arc Drill Nears Oil [73] Assignee: The United States of America as f- Test g In Drilling, March 1958, p g 106 represented by the Secretary of the and Navy, Washington, DC. Maurer, W. C.; Themal-Spalling, Chemical Drills; [22] Filed: Oct. 1, 1973 The Oil and Gas Journal, March 4, 1968, pp. 6973. Sarapau, E.; Electro-Energet1c Rock Breaklng Sys- PP 402,547 tems; Mining Congress Journal, June 1973, pp.

44-54. [52] US. Cl 175/15, 175/16, 175/17,

75 7 Primary Examiner-David H. Brown 51 lm. c1 E2lb 7/00 Attorney, Agent, or ch Sciascia; Joseph 58 Field of Search 175/15, 16, 17, 57, 65, St Amend; Darrell "01118 175/67 4 e e I [57] ABSTRACT. [5 6] References C'ted A method and apparatus for drilling a hole in rock. An 9 UNITED STATES PATENTS open-ended, hardened, drilling head containing 21 2,471,695 5/1949 McCullough 175/17 X means for creating high-intensity stress waves capable 2,822,148 2/1958 of spalling rock is utilized to drill the vhole. A fluid is 1 2,86 ,62 /1958 passed through the drilling head which removes the 3,036,645 5/1962 spalled rock from the drilling head. 3,500,942 3/1970 3,583,766 6/1971 7 Claims, 4 Drawing Figures 20 X l 2e 36' *1 Q 34 l STRESS WAVE DRILL BACKGROUND OF THE INVENTION niques. Cavitation is a phenomenon whereby under certain conditions cavities form and violently collapse within a liquid. A shock wave results from the cavitation and may cause considerable mechanical damage to neighboring solid surfaces. Cavitation is induced in a drilling liquid by any suitable technique such as by the generation of acoustic energy. The cavitation threshold is a function of the physical properties of'the liquid. The shock Wave pressure is a function of the cavitation threshold. Hence, the shock wave pressure is not easily controlled or varied. Liquids having differing physical propertiesare necessary for creating different shock wave pressures. Since the shock wave pressure necessary to cause spallingof rock varies with the physical properties of the rock, the cavitation method may require different liquids for different rock in order to ef 'fect spalling. Also, the range of shock wave pressures achievable by cavitation is limited by the physical properties of the liquid. Thus, certain types of rock are incapable of being spalled by cavitation.

Currently most rock drilling is done by rotary drag bits or percussion bits. In both of these methods a bit made of hardened steel or other hard material scrapes or impacts against the rock until the rock material is disintegrated into a powder. The efficiency of such drills is very low. The rate of drilling and-the cost increases greatly for hard formations and deep holes. In addition, the power lost in transmitting power to the rock reaches significant proportions.

The explosive drill, which is currently an operational alternative to rotary-percussion methods, is greatly restricted in application due to the high cost of explosive pellets.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide a stress wave drill for drilling rock whose shock wave pressure is easily controlled and varied, that does not require different liquids for different rock, whose shock wave pressure is not limited in'range, that is highly efficient, and that is more economical to operate than prior art drills. To achieve these significant advantages, one embodiment of the present invention providesa'n open-ended, hardened, drilling head containing an electro-hydraulic pulser. The electrohydraulic pulser creates high-intensity stress waves capable of spalling the rock. These high-intensity stress waves are transmitted to the surface of the rock by a liquid which also serves as a carrier to remove spalle'd rock from the borehole.

Accordingly, one object of the present invention is to Another object of the present invention is to provide a wide range of stress waves capable of spalling rock.

Another object of the present invention is to provide a highly efficient drill.

Another object of the present invention is to provide a highly economical drill.

Another object of the present invention is to provide a faster drilling rate.

Another object of the present invention is to provide drilling rates that are relatively independent of rock properties.

v Another object of the present invention is to increase the percentage of total power of a drill that is transmitted to the rock.

Other objects and a more complete appreciation of the present invention and its many attendant advantages will develop as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a top view of a specific embodiment of the present invention.

FIG. 4 is a front elevation of the specific embodiment of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to FIGS. 1 and 2, numeral 10 designates a drill stem. Attached to one end of drill stem 10 is an open-ended, hardened, drilling head 12. Hardened drilling head 12 is'flare'd slightly to prevent jamming of drill stem 10 in the borehole l4. Hardened drill head 12 must be capable of withstanding the stress waves generated byelectrohydraulic pulser 16 without cracking or breaking.

' Electrohydraulic pulser 16 comprises a solid block of electrical Electrode material 18. A high voltage electrode 20 extends through insulating material 18 and projects into the space inside .drilling head 12. Two ground electrodes 22, located adjacent to high voltage electrode 20, also extend through insulating material 18 and project into the space inside drilling head 12. Solid block l8.prevents short circuiting of the discharge between electrodes 20 and 22. Electrodes 20 and 22 are enclosed in electrical insulation 24 inside drill stem 10. The description and operation of electrohydraulic pulser 16 is promulgated in detail in Browne, Allen and Schrom, Electrohydraulics, Science Journal, March I968. ELECTRODE support material 26 supports and protects the electrodes 20 and 2-2 from impact with spalled rock being carried out of the borehole 14 by fluid 28.. Gasket 30 enables electro-hydraulic pulser 16 torota'te within drill stem 10and'drilling head 12. Gasket 30 forms a fluid-tight seal between electrohydraulic pulser l6 and drill stem l0and drilling-head l2.

Referring to' FIGS. 3- and 4, fluid 2s enters drill stem 10 via inlet port 34 and leaves drill stem 10 via outlet port 36. The direction of flowof fluid 28 is indicated by arrows 32. Fluid 28 serves as a carrier for spalled rock. Loose rock spalled by electrohydraulic pulser 16 is carried from the bottom of borehole 14 to outlet port 36, located near the top end of drill stem 10. Thus, the inside diameter of outlet port 36 must be large enough to pass the largest piece of spalled rock that will be produced by electrohydraulic pulser 16. The fluid 28 may be recycled through the drill provided the spalled rock is first removed therefrom. Electrohydraulic pulser 16 in conjunction with gasket 30 divides drill stem in two compartments 38 and 40. Of course, a plurality of compartments of various shapes are possible. The only requirement being that the compartments do not interrupt the fluid flow.

Shock waves from electrohydraulic pulser 16 travel through fluid 28 to the rock face 42. These stress waves load the face 42 which spalls on rebound. Rock particles spalled from the face 42 are removed by fluid 28 circulating through drill stem 10 and drilling head 12. The high-intensity stress waves generated by electrohydraulic pulser 16 are typically of microsecond duration. It is noted that electrohydraulic pulser 16 is but one means for generating high-intensity stress waves.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

We claim:

1. A stress wave drill for drilling a hole in rock comprising:

a drill stem having a first and a second end; a hardened drilling head having a first and a second open end, said first open end being connected to said second end of said drill stem;

means located in said hardened drilling head and said drill stem for generating high-intensity stress waves in said hardened drilling head capable of spalling the rock at the bottom of the hole;

means for dividing said drill stem into a plurality of compartments, each of which extends the entire length of said drill stem; and

interconnection means between said compartments 4 for injecting and retrieving a fluid, said fluid passing through said hardened drilling head, thereby carrying the spalled rock from the hole.

2. The drill of claim 1 wherein said second open end of said hardened drilling head is flared, thereby preventing said drill stem from jamming in the hole.

3. The drill of claim 1 wherein said means for generating stress waves is capable of controlled movement with respect to said drill pipe and said hardened drilling head about the longitudinal axis of said drill stem and said hardened drilling head.

4. The drill of claim 1 wherein said means for dividing said drill stem into a plurality of compartments comprises a single block of material dividing said drill stem into two compartments.

5. The drill of claim 1 wherein said means for generating stress waves comprises an electrohydraulic pulser.

6. The drill of claim 5 wherein said electrohydraulic pulser comprises:

a high voltage electrode;

a first ground electrode;

a second ground electrode;

means for electrically insulating said electrodes from said drilling head, said drill stem, and said fluid, except adjacent to the bottom of the hole, whereby said stress waves are created only in said hardened drilling head; ,and

said electrodes are supported and protected by said means for dividing said drill stem into a plurality of compartments.

7. The drill of claim 6 wherein said means for electrically insulating said electrodes includes:

a solid block of insulating material located in said hardened drilling head through which said electrodes extend, said electrodes protruding downward from said solid block of insulating material adjacent to the bottom of the hole, thereby preventing short-circuiting of the discharge, said solid block of insulating material only partially filling said hardened drilling head so that the flow of said fluid is not impeded. 

1. A stress wave drill for drilling a hole in rock comprising: a drill stem having a first and a second end; a hardened drilling head having a first and a second open end, said first open end being connected to said second end of said drill stem; means located in said hardened drilling head and said drill stem for generating high-intensity stress waves in said hardened drilling head capable of spalling the rock at the bottom of the hole; means for dividing said drill stem into a plurality of compartments, each of which extends the entire length of said drill stem; and interconnection means between said compartments for injecting and retrieving a fluid, said fluid passing through said hardened drilling head, thereby carrying the spalled rock from the hole.
 2. The drill of claim 1 wherein said second open end of said hardened drilling head is flared, thereby preventing said drill stem from jamming in the hole.
 3. The drill of claim 1 wherein said means for generating stress waves is capable of controlled movement with respect to said drill pipe and said hardened drilling head about the longitudinal axis of said drill stem and said hardened drilling head.
 4. The drill of claim 1 wherein said means for dividing said drill stem into a plurality of compartments comprises a single block of material dividing said drill stem into two compartments.
 5. The drill of claim 1 wherein said means for generating stress waves comprises an electrohydraulic pulser.
 6. The drill of claim 5 wherein said electrohydraulic pulser comprises: a high voltage electrode; a first ground electrode; a second ground electrode; means for electrically insulating said electrodes from said drilling head, said drill stem, and said fluid, except adjacent to the bottom of the hole, whereby said stress waves are created only in said hardened drilling head; and said electrodes are supported and protected by said means for dividing said drill stem into a plurality of compartments.
 7. The drill of claim 6 wherein said means for electrically insulating said electrodes includes: a solid block of insulating material located in said hardened drilling head through which said electrodes extend, said electrodes protruding downward from said solid block of insulating material adjacent to the bottom of the hole, thereby preventing short-circuiting of the discharge, said solid block of insulating material only partially filling said hardened drilling head so that the flow of said fluid is not impeded. 